Ticks and tocks

Last night while getting to sleep, I couldn't help but notice the sound of the second hand on my wall clock. I would have thought that the mechanism would produce an identical noise at each movement, but there is a discernible difference, much like the "tick-tock" used to describe the sound. So is there really a difference or am I just conditioned to hear one?

• The questioner doesn't say if the clock is electric or mechanical, old or modern, but I'm supposing it is a pendulum clock powered by a falling weight or a spring. It will have an escapement that converts the unidirectional force of the weight or spring into the oscillating impulses needed to keep the pendulum swinging (see diagram) – or the balance wheel for a compact clock or watch.

There are hundreds of escapement designs and they all make a noise each swing. But ...

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